1. Field of Invention
The present invention relates to a mask and fabrication method thereof and its application. More particularly, the present invention relates to a phase shift mask, PSM as well as its fabrication method and application.
2. Description of Related Art
The fabrication method of the conventional mask includes first providing a quartz substrate and a metal layer is formed on the quartz substrate. After then, a photoresist layer is formed over the quarts substrate and the metal layer. By performing light exposure and developing at the specific region, a portion of the photoresist layer is removed, so as to expose a portion of the metal layer, corresponding to the removed portion of the photoresist layer. Then, the exposed portion of the metal layer is removed by a dry etching process or a wet etching process. After the photoresist layer is completely removed, a light shielding pattern and a light transparent pattern are formed on the quartz substrate. A transparent pellicle layer is formed over. Then, a binary mask is accomplished.
Even though the binary mask is widely used in semiconductor fabrication, due to the disadvantage of poor precision for this mask, the precision of the photoresist pattern, which is formed by using the binary mask for light exposure, is affected. In order to solve this disadvantage, a phase shift mask is then proposed.
The conventional phase shift mask is formed by the similar fabrication processes for the binary mask. First, a binary mask is preliminarily accomplished. Then, a phase shift layer is formed over the binary mask. A photoresist layer is formed over the binary mask and the phase shift layer. After performing light exposure and developing at the specific region, a portion of the photoresist layer is removed for exposing the phase shift layer at the portion, corresponding to the removed portion of the photoresist layer. Then, the exposed portion of the phase shift layer is removed by a dry etching process or a wet etching process. After removing the photoresist layer, a transparent pellicle layer is formed over mask. The phase shift mask is accomplished. It should be noted that the material for the conventional phase shift layer is highly transparent material, such as quartz. Therefore, the only different between the light passing the phase shift layer and the light without passing the phase shift layer is the phase difference. The light intensity has no apparent difference.
Although the phase shift mask can solve the issue of poor resolution, however, due to the fabrication process including the etching process, the etching process has non-uniform etching on the phase shift layer, resulting in the non-uniform thickness for the phase shift layer on the mask. After the light passes the phase shift layer at the different positions of the mask, the transmittance or the phase angle may be different, resulting in poor yield for the photolithographic process.
In addition, the fabrication for the phase shift mask is further forming a phase shift layer over the mask after the binary mask is preliminarily accomplished. The phase shift layer is defined by the photolithographic process and then the pattern is transferred to the phase shift layer by the etching process. The photoresist layer is then completely removed. Comparing with the conventional binary mask, since it has more fabrication processes, the probability for defects occurring on fabricating the mask is increasing. This would cause the higher cost for fabricating the mask.